Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!usc!cs.utexas.edu!uunet!yale!Duchier-Denys
From: Duchier-Denys@cs.yale.edu (Denys Duchier)
Newsgroups: comp.emacs
Subject: Re: Lisp Programming: Substring Searches, etc.
Keywords: lisp substring searches case statements
Message-ID: <65891@yale-celray.yale.UUCP>
Date: 9 Jul 89 18:07:16 GMT
References: <397@lxn.eds.com>
Sender: root@yale.UUCP
Reply-To: Duchier-Denys@cs.yale.edu (Denys Duchier)
Organization: Computer Science, Yale University, New Haven, CT 06520-2158
Lines: 28
In-reply-to: chris@lxn.eds.com (Christopher D. Orr)

(defun extract-file-extension (filename)
  (and (string-match ".+\\.\\(.*\\)$" filename)
       (substring filename (match-beginning 1) (match-end 1))))

after setting file-ext to the proper file extension you could do
something like this:

(cond ((string-equal file-ext "c") ...)
      ((string-equal file-ext "h") ...)
      ...
      (t ...))

Perhaps it would be best to define a function like the following

(defun act-according-to-extension ()
  (let ((file-ext (extract-file-extension buffer-file-name)))
    (cond ((string-equal file-ext "c") ...)
          ((string-equal file-ext "h") ...)
          ...
          (t ...))))

and then do

(setq find-file-hooks (cons 'act-according-to-extension find-file-hooks))

You should look up the documentation for find-file-hooks and auto-mode-alist

--Denys